Astatine
[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵ · 2 · 8 · 18 · 32 · 18 · 7
The rarest naturally occurring element on Earth: less than a gram exists in the whole crust at any moment. Astatine is so unstable that a macroscopic sample would instantly vaporise from its own decay heat.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 85
- Atomic mass
- 210 а.е.м. ≈
- Electron configuration
- [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵
- Electrons per shell
- 2 · 8 · 18 · 32 · 18 · 7
- Block
- p-block
- Group
- Halogens
- Period
- 6
- Electronegativity (Pauling)
- 2.2
- Electronegativity (Allen)
- 2.39
- Atomic radius
- 127 pm
- Covalent radius
- 150 pm
- Van der Waals radius
- 202 pm
- Ionisation energy 1
- 899 kJ/mol
- Electron affinity
- 270.1 kJ/mol
- Common oxidation states
- -1, +1
- Oxidation states
- -1, +1, +3, +5, +7
Physical properties
- State at 25 °C
- solid
- Density
- 6.35 g/cm³ ≈
- Melting point
- 575 K · 301.9 °C ≈
- Boiling point
- 610 K · 336.9 °C ≈
- Speed of sound
- no data
Thermal properties
- Heat of fusion
- 6 kJ/mol ≈
- Heat of vaporisation
- 40 kJ/mol ≈
- Specific heat capacity
- no data
- Thermal conductivity
- 1.7 W/(m·K) ≈
Mechanical properties
- Young's modulus
- no data
- Shear modulus
- no data
- Bulk modulus
- no data
- Poisson ratio
- no data
- Mohs hardness
- no data
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- no data
- Magnetic ordering
- non-magnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- no data
- Lattice constants
- no data
Abundance
- In the crust
- does not occur
- In the ocean
- no data
- In the universe
- no data
- In the human body
- no data
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 210At | — | 8.1 h | ЭЗ |
| 211At | — | 7.21 h | ЭЗ, α |
The longest-lived isotope is astatine-210 at 8.1 hours. Astatine-211, half-life 7.2 hours, is the only one of medical interest.
Discovery
- Year of discovery
- 1940
- Discovered by
- Corson, MacKenzie and Segrè
- Where
- USA
- Origin of the name
- from Greek astatos (unstable)
History
Corson, MacKenzie and Segrè synthesised astatine in 1940 by bombarding bismuth with alpha particles in a cyclotron. The name means unstable.
Where it occurs
Formed in traces within the uranium and thorium series. Estimates put under 25 grams of astatine on the entire planet at once.
How it is produced
Only in a cyclotron, by alpha bombardment of bismuth-209. Work proceeds in nanograms.
Role in living things
No biological role. As a halogen astatine concentrates in the thyroid much as iodine does.
Safety
Extremely radiotoxic. All work is done remotely with microscopic quantities.
Uses
- Astatine-211 under study for targeted alpha therapy: an alpha particle kills a cell without touching its neighbours
- Studying halogen chemistry at the heavy-element limit
Curiosities
- Astatine is the rarest naturally occurring element on Earth.
- No human has ever seen astatine: a visible sample would boil away from its own radioactive heating.
- Every astatine property in the reference books is calculated or extrapolated.
- The name means, literally, unstable.